This invention relates to semiconductor devices and more particularly to majority carrier rectifying barrier devices.
Schottky barriers, p-n junctions and lattice matched heterojunctions are the three basic types of rectifying structures whose potential barrier heights are fixed by interface states and electron affinity and bandgap differences which impose restrictions in their utilization for electronic devices. In addition, majority carrier devices are necessary where speed requirements prohibit minority carrier current transport.
Although Schottky barriers are used almost exclusively for very high frequency switching, mixing and rectifying applications they exhibit several inherent limitations. For example, for a particular metal-semiconductor system, barrier heights are virtually constant and operational stability is related to metallurgy of the contact system. Interface states and interfacial layers play a dominant role in determining the Schottky barrier transport properties which can lead to undesirable hysteresis effects particularly in metal-GaAs structures. Attempts have been made in the past to modify the heights of Schottky barriers by implanting n and p type regions near the semiconductive surface and more recently rectification has been observed in a structure using implanted n.sup.+ and p.sup.+ regions in lightly doped n type silicon. Also known is a unipolar rectifying structure having a triangular potential barrier which has been induced by a graded layer of Al.sub.x Ga.sub.1-x As.
In signal mixer applications for operation in the near millimeter wave frequency band, Schottky barrier devices typically used exhibits relatively large barrier heights which necessitates the use of relatively high local oscillator power. On the other hand, point contact devices exhibiting relatively low barrier heights require a delicate and time consuming formation process providing a relatively low yield during fabrication accompanied by erratic reproducability.
Accordingly, it is an object of the present invention to provide an improvement in semiconductive devices having a rectifying barrier.
Another object of the present invention is to provide a semiconductor barrier device having a relatively low barrier height.
Still another object of the present invention is to provide a semiconductor barrier device whose barrier height is variable.
And yet another object of the present invention is to provide a semiconductor device having a rectifying barrier whose characteristics can be continuously and independently controlled.